Defroster



March 6, @340 w. A. KUENZLH ET AL DEFROSTER Filed. June 29, 1931 I N VEN TORS.

Wmwer A. Kuenzi y @de EPIoeger Patented Mar. 6, 1934 UNITED STATES PATENT OFFICE DEFROSTER Application June 29, 1931, Serial No. 547,636 16 Claim- .(Cl- 172-239) This invention relates to refrigerating systems employing a volatile refrigerant which is liquefied in a condensing unit and supplied to an evaporator in which the liquid evaporates absorbing heat from the medium to be cooled and the vapor is r intervals.

of personal attendance and detracts from the full returned to the condensing unit.

In such refrigerating systems the operation of the condensing unit is usually intermittent, the control being responsive to the temperature of the medium to be cooled, the temperature of the evaporator, or the pressure in the evaporator. During operation of the condensing unit the temperature and pressure of the refrigerant in the evaporator are lowered to predetermined minimum values and during the idle period of the condensing unit the temperature and pressure of the refrigerant in the evaporator rise to predetermined maximum values.

If the maximum temperature is maintained below freezing the evaporator gradually accumulates a covering of frost at a rate depending upon the amount of moisture in the medium being re fn'gerated and the amount of circulation of the medium. If the accumulation of frost on the evaporator is not prevented or regularly removed the efficiency of the system becomes seriously impaired.

Several methods and devices for the removal of frost from the evaporator, commonly referred to as defrosting, have been proposed. For instance, if the maximum temperature limit of the evaporator is sufficiently high defrosting will occur during each cycle, that is, the frost will melt during part of the idle period of the condensing unit. It has also been proposed to intermittently apply heat to the evaporator to melt the frost accumulation. The ineiliciencies of such methods are at once apparent.

Defrosting has also been accomplished by manually stopping the compressing unit for a sufficient length of time or by various manually operated devices for increasing the length of the idle period of the compressing unit at desired This, of course, presents the feature automatic operation of the refrigerating apparatus.

Automatic devices have been proposed which operate in conjunction with the temperature or pressure control element for the condensing unit whereby the operation of the control is modified to increase an idle period of the condensing unit in predetermined sequence. Such devices require modified construction of the control element and also introduce difficulties in the proper adjust ment of the control element.

In accordance with this invention defrosting is accomplished by periodically increasing an idle period of the condensing unit whereby the evaporator temperature rises above the usual mo ximum limit for a length of time suilicient to allow the accumulated frost to melt. This is accomplished by a device entirely separate from the control element thereby eliminating all complications or; such as the necessity of modifying present types of control elements; the possibility of affecting reliable operation of the control element; and the difficulty of supplying a defrosting device as extra equipment.

Other objects and advantages will be apparent from the following description taken in conneo tion with the accompanying drawing, wherein,

Fig. l is a diagrammatic view illustrating one application of the invention;

Fig. 2, a fragmentary detail, top plan view, on the line 2--2 of Fig. 1, illustrating the operating and holding pawls and associated rack; and

Fig. 3. a view similar to that of Fig. 1 with can tain of the parts in operated positions.

Referring to the drawing, an electric motor 10 drives the compressor of a condensing unit which is part of a well known refrigerating system. not shown. The motor is a single phase type with a split phase starting winding and is controlled so by the usual motor starting switch 11 responsive to the temperature or pressure of the evaporator, as is well known in the art.

A separate defrosting control contemplated by this invention comprises a rack 12 urged to a normal position by a spring 13. A pawl 14 piv oted at 15 on one end of the armature 16 of an electromagnetic relay 1'? normally engages the teeth of rack 12. The armature 16 is normally retained in its retracted position by a spring 18 which is stronger than the spring 13 which tensions the rack 12. The operating coil 19 of relay 1? is connected across the circuit of the main or running winding of the motor 10 so that it is en ergized while the motor control switch 11 is closed.

During operation of the refrigerating system the relay coil 19 is energized at the start of each operating period attracting armature 16 against the action of spring 18, whereupon the pawl 14 is drawn back one notch or tooth along the rack 12. During this time the rack is maintained in position against the action of spring 13 by a holding pawl 20 mounted on a fixed pivot 31 as best shown in Fig. 2. When switch 11 operates no to stop the motor 10 at the end of each operating period, coil 19 is de-energized releasing armature 16, whereupon pawl 14, under the action of spring 18, moves rack 12 one notch or tooth, the movement being limited by stop 30.

A switch 21 having normally closed contacts 22 and normally open contacts 23 is operated by rack 12 after it has been displaced the number of notches corresponding to the desired number of operating periods of the motor. When switch 21 is operated the contacts 22 are open and contacts 23 are closed. Contacts 22 are connected in series with the running winding of motor 10 and contacts 23 are connected in series with heating coil 24 of the thermostatic element 25, which heating coil is connected across the current supply line 26 to the motor. Thermostatic element 25 is connected through rod 27 to pawl 14 so that upon operation of the thermostatic element responsive to the heating of coil 24 the pawl 14 is lifted clear of the rack 12 carrying with it pawl 20 by means of the projecting boss 28 on pawl 14 engaging pin 29 on the pawl 20. When the pawls are disengaged the rack 12 is retracted to its normal position by spring 13 thus releasing switch 21.

When switch 21 is operated after a predetermined number of operating periods of the motor as described above, the opening of contacts 22 opens the motor circuit and closing the contacts 23 closes the circuit to the heating coil 24. Since the rack 12 is only stepped over when coil 19 is de-energized, switch 21 is operated at the end of an operating period when switch 11 is opened. Therefore, no current is supplied to the heating coil 24 until the beginning of the next normal operating period when switch 11 is closed. At this time the motor will not start since contacts 22 are open and, depending upon the adjustment of the thermostat and the design of heating coil 24, more time must elapse before the thermostat operates to raise the pawls to release switch 21. as previously described. During this extended idle period the temperature in the evaporator of the refrigerating system rises sufliciently to allow defrosting.

When the thermostat finally operates and switch 21 is released the motor circuit is closed through contacts 22 upon which the motor begins operation and the heating coil circuit through contacts 23 is opened allowing the thermostat to cool, and the pawls 14 and 20 are again lowered into engagement with rack 12 which has been retracted to its normal position by spring 13 and the sequence is repeated.

It will be obvious to those skilled in the art that various other changes may be made in the construction and arrangement without departing from the spirit of the invention and therefore the invention is not limited to what is described in the specification and shown in the claims but only as indicated in the appended drawing.

We claim:

1. In refrigerating apparatus operated by an electric motor, a defrosting device comprising a normally closed switch in said motor circuit. means for opening said switch responsive to and at the end of a predetermined number of motor operating periods, and means operative upon instigation of the next succeeding operating period to close said switch after a time interval.

2. In refrigerating apparatus operated by an electric motor, a device for periodically increasing an idle period of said apparatus to allow defrosting comprising, a normally closed switch in said motor circuit, means for opening said switch responsive to and at the end of a predetermined number of motor operating periods, and means operative upon the opening of said switch for releasing the first said means to close said switch a time interval after instigation of the next succeeding operating period.

3. In refrigerating apparatus operated by a single phase electric motor, a defrosting device comprising a normally closed switch in series with the runnnig winding of said motor, means for opening said switch responsive to and at the end of a predetermined number of motor operating periods, and a time delay device operative upon both the opening of said switch and the instigation of the next succeeding operating period for releasing the first said means to close said switch.

4. In refrigerating apparatus operated by a single phase electric motor having a starting switch operated responsive to a refrigerating requirement of the apparatus, a defrosting device comprising a normally closed switch in the running winding circuit of said motor, means for opening said normally closed switch responsive to and at the end of a predetermined number of motor operating periods, and time delay means operative upon both the opening of said normally closed switch and the closing of said motor starting switch for releasing the first said means to 'close said normally closed switch.

5. In refrigerating apparatus operated by an electric motor, a starting switch for said motor, and a defrosting device comprising a normally closed switch in said motor circuit, an electromagnetic device connected in said motor circuit for opening said normally closed switch after a predetermined number of operating periods, a thermostatic device for releasing said normally closed switch and re-setting said electromagnetic device, and a heating coil for said thermostatic device connected upon the opening of said nor mally closed switch to be energized upon closing of said starting switch.

6. In refrigerating apparatus operated by a single phase electric motor, a starting switch for said motor, and a defrosting device comprising a normally closed switch in series with the running winding of said motor, an electromagnetic device connected in parallel with the running winding of said motor for opening said normally closed switch after a predetermined number of motor operating periods, a thermostatic element for reclosing said normally closed switch and resetting said electromagnetic device, and a heating coil for said thermostatic element connected upon the opening of said normally closed switch to be energized upon closing of said starting switch.

7. In refrigerating apparatus operated by a single phase electric motor, a defrosting device comprising a normally closed switch in series with the running winding of said motor, an electromagnetic device for opening said switch after a predetermined number of motor operating periods, and a time delay device operative upon both the opening of said switch and the instigation of the succeeding motor operating period for closing said switch and resetting said electromagnetic device.

8. For refrigerating apparatus operating means including an electric motor, a starting switch for said motor operated responsive to refrigerating requirements of the apparatus, a normally closed switch in said motor circuit, step by step mechanism for opening said last switch upon a predetermined number of operations, an electromagnetic relay energized when said motor starting switch is closed for advancing said mechanism, and a time delay device operative only upon both the opening of said normally closed switch and the closing of said starting switch for resetting said step by step mechanism.

9. For refrigerating apparatus operating means including an electric driving motor, a starting switch for said motor responsive to refrigerating requirements of the apparatus, a normally closed switch in said motor circuit, step by step mechanism for opening said last switch upon a predetermined number of operations, an electromagnetic relay connected in said motor circuit for advancing said mechanism, a thermostatic element operative to reset said step by step mechanism, and a heating coil for said thermostatic element connected upon the opening of said normally closed switch to be energized upon closing of said starting switch.

10. For refrigerating apparatus operating means including an electric motor, a starting switch for said motor operative responsive to refrigerating requirements of the apparatus, a second switch having a set of normally closed and a set of normally open contacts, said normally closed contacts being connected in series with the running winding of said motor, step by step mechanism for operating said second switch upon a predetermined number of operations of the mechanism, an electromagnetic relay for advancing said mechanism and connected across the running winding of said motor, a thermostatic element operative to reset said mechanism, and a heating coil for said thermostatic element connected to the source of current through said normally open contacts and said starting switch.

11. For refrigerating apparatus operating means including an electric motor, a starting switch for said motor operated responsive to refrigerating requirements of the apparatus, a second switch having a set of normally closed and a set of normally open contacts, the normally closed contacts being connected in series with the running winding of said motor, a rack urged to a normal position by a spring and adapted to operate said second switch in its displaced or operating position, an actuating pawl engaging said rack, a holding pawl engaging said rack, an electromagnetic relay connected across the running winding of said motor for retracting said actuating pawl, a thermostatic element operative to disengage said pawls allowing the rack to return to its normal position, and a heating coil for said thermostatic element connected to the source of current through said normally open contacts and said starting switch.

12. For refrigerating apparatus operating means including an electric motor, a starting switch for said motor operated responsive to refrigerating requirements of the apparatus, and a defrosting device comprising a switch having a set of normally closed and a set of normally open contacts, said normally closed contacts being connected in series with the running winding of said motor, a rack urged to a normal position by a spring and adapted to operate said switch in its displaced or operating position, a spring tensioned actuating pawl engaging said rack, a holding pawl engaging said rack, an electromagnetic device to retract said actuating pawl and comiected to the source of current through said motor starting switch, a thermostatic element operative to disengage said pawls allowing the rack to return to its normal position, and a heating coil for said element connected to the source of current through said normally open contacts and said starting switch.

13. In combination with operating means for refrigerating apparatus having a single phase electric motor and a starting switch for said motor, a defrosting device comprising a normally closed switch in series with the running winding of said motor, a normally open switch, a rack urged to a normal position and adapted to simultaneously operate said switches in its displaced or operating position, an actuating pawl engag ing said rack, a holding pawl engaging said rack, an electromagnetic device forretracting said actuating pawl connected to the source of current through said motor starting switch, a thermostatic element operative to disengage said pawls allowing the rack to return to its normal position, and a heating coil for said element connected to the source of current through said normally open switch and said motor starting switch.

14. Operating means for refrigerating appa ratus having an electric motor and a starting switch for said motor, a defrosting device comprising a switch having a set of normally closed and a set of normally open contacts, said normally closed contacts being connected to open said motor circuit, a rack urged to a normal position by a spring and adapted to operate said switch in a displaced or operating position, a first pawl engaging said rack, a holding pawl also engaging said rack, an electromagnetic relay connected to the source of current through said motor starting switch for retracting said first pawl, means for actuating said first pawl upon de-energization of said relay thereby displacing said rack one notch or step toward its switch operating position, a thermostatic element operative to disengage said pawls allowing the rack to return to its normal position, and a heating coil for said thermostatic element connected to the source of current through said normally open contacts and said motor starting switch.

15. In refrigeration apparatus operated by an electric motor, a starting switch for said motor operative responsive to refrigeration requirements of the apparatus, and a defrosting device comprising means for opening the circuit of said motor responsive to and at the end of a predetermined number of motor operating periods, and means operative upon the next succeeding closure of said starting switch to close said motor circuit after a time interval.

16. In refrigeration apparatus operated by an electric motor, a defrosting device comprising means for opening the circuit of said motor responsive to and at the end of a predetermined number of motor operating periods, and means operative upon instigation of the next succeeding operating period to close said motor circuit after a time interval.

WALTER A. KUENZLI. CLYDE E. PLOEGER. 

